1. Field of the Invention
The present invention relates to a joystick controller typically used for controlling heavy machinery, industrial equipment and the like. The invention relates more specifically to an improved joystick controller which employs strain gauges which are placed in tension and compression to indicate the position and direction of a moveable post.
2. Background Art
Joystick controllers or actuators provide an electrical signal responsive to the displacement of a rod or lever from a neutral position. Preferably, they permit accurate manifestations of lever movement in any direction (i.e., 360°) by generating signals along two orthogonal exes (i.e., x and y) based upon the respective displacement along each axis. Typically, they utilize variable resistors coupled to the lever through complex mechanical assemblies. Various examples of such assemblies are shown in prior art U.S. Pat. Nos. 4,306,208; 4,459,440; 4,587,510; 4,849,583; 5,229,742; and 6,618,036.
A variety of joysticks have been used to input commands to video game controllers or to control the motion of a cursor on a video screen. Examples include U.S. Pat. No. 4,488,017 to Lee and U.S. Pat. No. 4,501,939 to Hyltin et al. Devices of this type employ electrical contacts or switches which are actuated by motion of the joystick shaft. Most of these joysticks are able to sense the motion of the shaft in one of four or eight different radial directions but do not sense how far the shaft has moved in the chosen direction. The output signal is digital in the sense that each contact or switch actuated by the shaft motion is either open on closed. However, the digital resolution is exceedingly low (one binary bit of information for each of the eight detectable directions of shaft motion). Also, the electrical contacts in mechanically operated switches are subject to wear, corrosion, contamination, pitting and contact bounce. Joysticks of this type lack the resolution and reliability needed for control of powered wheelchairs, forklifts, machine tools, earth-moving machines, robotic devices, etc.
In an effort to achieve the very high resolution of joysticks employing resistive potentiometers while overcoming their well known reliability problems non-contact analog joysticks have been developed. Some use inductive techniques while others exploit optoelectronic devices. U.S. Pat. No. 4,658,678 to Frederiksen and U.S. Pat. No. 4,855,704 to Betz disclose joysticks in which motion of the shaft alters the inductance of a coil which is part of an oscillator circuit. Then, a property of the oscillator (frequency, amplitude or phase) is processed electronically to obtain an indication of shaft position. Variable transformer coupling between an excitation coil, moved by the joystick shaft, and fixed sensor coils is employed in U.S. Pat. No. 4,434,412 to obtain an analog signal indicative of shaft position. These approaches are more reliable than resistive potentiometers but are inherently non-linear (i.e., unlike resistive potentiometers which are normally fabricated to be very linear, the analog output signal from these inductive devices does not vary linearly with joystick shaft position). Electronic compensation of this inherent non-linearity is feasible but adds to cost and complexity. Furthermore, the analog signal must be processed through interface circuitry, typically including an analog-to-digital converter, before it can be used in a modern control system, almost all of which use digital microprocessors or microcomputers.
Thus, it can be seen that mechanical assemblies for analog joysticks tend to be mechanically complex and electrical assemblies for digital joysticks tend to be electronically complex. Both such complexities increase cost and reduce reliability. One solution to these disadvantages of the prior art is to employ joysticks using strain gauges.
In joystick assemblies, strain gauges are used to measure the force and the direction of the force applied to the joystick by the user. Such prior art joystick assemblies utilize a joystick support structure that is deflected or strained by the joystick. One example of a prior art joystick that employs strain gauges is disclosed in U.S. Pat. No. 5,325,081. However, this patent teaches an assembly wherein strain gauges are formed on spring-like planar surfaces that form a square tube around the joystick lever. This approach limits lever movement and generates material fatigue that can lead to reliability problems.
Another prior art joystick controller is disclosed herein in FIGS. 1-3. This controller solved many of the noted deficiencies of the patent art, but introduced end of travel anomalies that detracted from overall performance as will be described hereinafter.
Thus, there is still a need for a new type of joystick that overcomes the noted deficiencies of the prior art relating primarily to complexity, cost and reliability.